The carbon nanotubes (CNT) are cylindrical structures whose wall has the chemical composition and the disposition of graphite, for these features they are considered to be formed by rolled graphite. The CNT exist with a single wall, known as single walled CNT or SWCNT by their abbreviations in English, or multiple walled, MWCNT by their abbreviation in English.
The mass production interest of these nanotubes has risen because of the development of several applications in the materials field, such as fiber components, as an additive to improve mechanical properties or electrical conduction, or as a component in the electronic and optoelectronic product integration.
As mentioned by Resasco (U.S. Pat. No. 6,413,487), there are three conventional methods for the massive synthesis of carbon nanotubes. The first one is the production by using electric arc, that generally requires the use of graphite electrodes (U.S. Pat. Nos. 6,884,404, 7,244,408, or US Patent Application Publication No. 2001/00502219).
Another method widely known is based on the use of particles from which the CNT grow; enabling these particles to be deposited in a substrate or being in suspension through a fluidized bed (U.S. Pat. Nos. 6,413,487; 6,730,284; 6,919,064; 6,955,800; and US Patent Publications Nos. 2001/0053344, 2004/0149209, 2004/151654, and 2006/0039849).
Finally, a third method frequently used is the formation of CNT in a surface under controlled temperature in which simultaneously are fed a CNT precursor that donates the carbon and a molecule that donates a metallic element that acts as a catalyst to promote the organization of the hydrocarbon to form the graphite walls. This method is called spray pyrolysis. Jacques and Andrews (U.S. Pat. No. 7,160,531) developed a method using this principle, in which the production is performed by using a conveyor belt having the flat pieces that are used as a substrate for the growth of the CNT. In order to spray the solution containing the precursor and catalyst, a porous medium is used, which according to the inventors allows the regulation of the diameter of the formed CNT. Finally the piece in which the CNT is formed is taken to another area where the CNT are removed by mechanical form or by ultrasound.